(24b) Production of High-Quality Carbon Fiber from Lignin Precursor

Lignin is considered as a promising precursor material for producing low-cost green carbon fiber due to its abundant availability at low costs and high aromatic content. Unfortunately, lignin-based carbon fibers are difficult to commercialize due to their poor mechanical properties. Lignin-based carbon fiber is usually made using a fabrication process previously developed to convert polyacrylonitrile into carbon fibers, despite that the precursor materials have very different chemical structures. The questions regarding lignin-based carbon fiber, such as how the physical and chemical properties of lignin change during the fiber oxidation and subsequent carbonization, and how these property changes affect the mechanical properties of the final products, remain unclear to date. Due to the lack of the fundamental insights into lignin transformation, previous approaches to improve the quality of the carbon fiber has been largely unsuccessful. In this study, carbon fibers were produced from softwood-derived organosolv lignin using a melt-spinning method. The fibers at different stages of the fabrication were carefully investigated using comprehensive analytic techniques to elucidate the relationships between the chemical structure and material properties of the fiber relevant to the fiber fabrication conditions. The results showed that applying tension can significantly modify the chemical structure of the lignin fiber during oxidation and carbonization, thus leading to carbon fibers with unique carbon structures and strong tensile properties. In our study, the average tensile strength and tensile modulus of the carbon fiber reached 1.96 GPa and 158 GPa with a carbonization temperature of 700 °C, and 2.12 GPa and 164 GPa with a temperature of 800 °C, respectively. Our research finding suggested that a good understanding about chemical structure and material property correlation is a key to develop high-quality carbon fiber using lignin.